1
The Science of Stick-Slip
IADC Stick-Slip Mitigation Workshop
July 15, 2010
John Macpherson Baker Hughes Inc.
2 Bending Bending Bending Whirl Whirl Whirl Lateral Vibration Stick-Slip Stick
Stick--SlipSlip Torsional Vibration Bit Bounce Bit Bounce Bit Bounce Axial Vibration Jarring (impact) Jarring (impact) Jarring (impact)
Torsional Vibrations
•
Drillstring is a Spring-Mass System (Torsional Pendulum)
•
Torsional Oscillation frequency
is the first natural torsional
frequency for the drillstring
System
•
Frequency is very low, usually
less than 1/2 Hz, for a drillstring
of any length.
Torsional Oscillation Period
• Analytic Calculation: Bailey J.J., and Finnie I., "An Analytical Study of Drill-String Vibration", Trans. ASME, May 1960, pp 122-128
•
• Empirical: period of oscillation increases by 2 seconds per 1,000m of 5” pipe (Dufeyte and Empirical:
Henneuse, 1991, IADC/SPE 21945) 0 2 4 6 8 10 12 14 0 5000 10000 15000 20000 25000 30000 6-3/4 x 200 ft BHA 8-1/4 x 200 ft BHA
Drillstring Length, feet
Drillstring Length, feet
Torsional Oscillation Period, seconds
Torsional Vibrations
Bit Rotation Rate
A B C
• A – Increase RPM, B – Torsional Oscillations, C – Stick-Slip (period = 4.5s)
Smooth rotation Torsional Oscillations Stick-Slip
Stick-Slip: bit rotation periodically stalls during continuous surface rotation.
Stick
Stick--Slip: bit rotation periodically stalls during continuous surface Slip: bit rotation periodically stalls during continuous surface rotation.rotation.
Time (secs)
Severe Stick Slip
200 250 300 350 400 600 400 200 0 Time (seconds) 0 10 20 30 50 100 150 kN.m kN Stick periods 24 s rotation periods 2.5s Maximum DRPM 645; Surface 70 -165 RPM for 1.4s Increase RPMStick-Slip Example Roller Cone Bit
15 10 0 5 -5 400 300 200 100 0 -100 100 50 0 320 330 340 350 360 370 Weight, kN Torque , kN.m RPMElapsed Time, seconds
• Downhole Rotation Rate
Modeling: Stick-Slip Visualization
Downhole torsional oscillations and stick-slip behavior are visible as periodic torque fluctuations on surface
Downhole torsional oscillations and stick
Downhole torsional oscillations and stick--slip behavior are visible slip behavior are visible as periodic torque fluctuations on surface
as periodic torque fluctuations on surface
•
•
Drillstring Simulation
Drillstring Simulation
– Finite Element Model
– Arbitrary curved and
straight boreholes
– String can move freely in
wellbore
– Wall contact penalty
formulation
– Friction during drillstring-
wall contact
– Torque on bit from a
Bit and Drillstring Coupled Modeling
• Bit interaction with rock (rock
properties) important
• Validated with high frequency
downhole measurements
• “Falling friction” characteristic
• Stribeck type bit-friction model
0 50 100 150 200 0 3000 6000 9000 Rotational Speed [RPM] To rq u e o n B it [N m ] 0 5 10 15 20 0 3000 6000 9000 T o rque on B it [ N m] T ime [s] 0 5 10 15 20 0 100 200 T ime [s] R ot a ti ona l S pe e d [ R P M ] Measurement Simulation B B B n n T 5231.608100.658 49.91
Reckmann, Jogi, Herbig, 2007,
Reckmann, Jogi, Herbig, 2007, ““USING DYNAMICS MEASUREMENTS WHILE DRILLING TO DETECT LITHOLOGY CUSING DYNAMICS MEASUREMENTS WHILE DRILLING TO DETECT LITHOLOGY CHANGES HANGES
AND TO MODEL DRILLING DYNAMICS
AND TO MODEL DRILLING DYNAMICS””, paper 29710, OMAE, 26, paper 29710, OMAE, 26th thInternational ConferenceInternational Conference
Comparison of measurements and simulation for the Stribeck type bit
model
Comparison of measurements and
Comparison of measurements and
simulation for the Stribeck type bit
simulation for the Stribeck type bit
model
• Stick-slip likely when operating in region of “falling friction”
• Increase RPM to reduce likelihood of stick-slip
Bit and Drillstring Coupled Modeling
Stick-Slip Likely Stick-Slip Unlikely
Reckmann, Jogi, Herbig, 2007,
Reckmann, Jogi, Herbig, 2007, ““USING DYNAMICS MEASUREMENTS WHILE DRILLING TO DETECT LITHOLOGY CUSING DYNAMICS MEASUREMENTS WHILE DRILLING TO DETECT LITHOLOGY CHANGES HANGES
AND TO MODEL DRILLING DYNAMICS
Measuring Stick-Slip Downhole: Stick-Slip Index
RPM
RPM
RPM
SSI
avg
2
min
max
RPM A B CSSI
0 0.1 0.1 inc to 1.0 > 1.0• A – Increase RPM, B – Torsional Oscillations, C – Stick-Slip (period = 4.5s) SSI is encoded in a few bits and transmitted to surface
SSI is encoded in a few bits and transmitted to surface
CoPilot Memory Depth Log
CoPilot Memory Depth Log
Surf WOB Surf WOB klbf klbf DH WOB DH WOB klbf klbf Surf TRQ Surf TRQ ftlb ftlb DH TRQ DH TRQ ftlb ftlb Surf RPM Surf RPM Max RPM Max RPM RPM RPM Avg RPM Avg RPM RPM RPM Min RPM Min RPM RPM RPM S Slip Severity S Slip Severity Tangential Vib Tangential Vib gravity gravity Bit Bounce Bit Bounce Axial Vib Axial Vib gravity gravity Whirl Severity Whirl Severity Lateral Vib Lateral Vib gravity gravity Stick-Slip Severity Min, Max, Average RPM DH and SURF Torque DH and SURF WOB Axial Vibration Severity Lateral Vib Severity
Example MWD Memory Log showing wellbore friction and stick-slip
Example MWD Memory Log showing
Example MWD Memory Log showing
wellbore friction and stick
Stick-Slip: Relationship to Failure
•
•
MWD Components
MWD Components
– 2010 study, IADC/SPE 127413
– Significant relationship to MWD tool failures:
1. Lateral Acceleration Peak Energy
2. Lateral Acceleration 1s RMS Energy
3. Cumulative RPM Variation (revolutions)
4. Cumulative Backward Whirl
5. Cumulative Stick-Slip Index
•
•
PDC Bits
PDC Bits
– May be damaged during stick-slip
– Center of rotation off the center of the bit
– Cutters on some part of the bit move
backwards for some portion of a revolution
Stick-Slip: Recognition and Control
•
•
Measurement Downhole
Measurement Downhole
– Measure rotation rate of drillstring
– Magnetometers and/or centripetal acceleration
– Bit periodically stalls (MWD diagnostic transmission)
•
•
Measurement on Surface
Measurement on Surface
– Rotary torque & rotary speed
– Large periodic fluctuations in torque
•
•
Stick
Stick
-
-
Slip Control
Slip Control
– Manual (follow flow charts)
1. Reduce WOB, increase RPM
2. Stop drilling, restart with decreased WOB, increased RPM
– Automatic
• Soft-torque stick-slip control systems
• Modifies drive speed control to reduce torsional fluctuations
– Downhole / Autonomous
0 2 Stick-Slip Index 0 20 40 60 L ate ra l V ib ra tio n (g ) 1
Downhole Data Distribution for 219 MWD runs
Downhole Data Distribution for 219 MWD runs
Fully Developed Stick
Fully Developed Stick--SlipSlip
1
Sliding
Sliding
Reckmann etal 2010,
Reckmann etal 2010, ““MWD Failure Rates Due to Drilling DynamicsMWD Failure Rates Due to Drilling Dynamics””, IADC/SPE 127413, IADC/SPE 127413
Contours showing data sets with average ROP in excess of 45 ft/hr, overlaid on colored surface defined by Stick-Slip Index and Maximum Lateral Acceleration.
0 2 Stick-Slip Index 0 20 40 60 la te ra l V ib ra tio n (g ) Sliding
Sliding Fully Developed StickFully Developed Stick--SlipSlip
High ROP Low Laterals Moderate SSI High ROP Mod Laterals Low SSI
Downhole Data Distribution for 219 MWD runs
Downhole Data Distribution for 219 MWD runs
Stick-Slip, Lateral Vibrations and ROP
Reckmann etal 2010,
The Science of Stick-Slip – Conclusions
– Torsional drillstring behavior includes both torsional oscillations and stick- slip. In stick-slip the bit periodically stalls in rotation
– Stick-slip is detrimental to drill bits, and sustained stick-slip can be damaging to MWD components
– Stick-slip behavior is relatively well understood, can be modeled, and can be recognized both downhole and on surface while drilling
– Stick-slip behavior can be mitigated manually, automatically, and using downhole subs
– Removing torsional oscillations from the system will result in the BHA
being susceptible to high lateral vibrations, which could result in rapid
